Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Using a polyclonal antiserum raised against the inositol 1,4,5-trisphosphate receptor (IP3R) purified from rat cerebellum, we examined the subcellular distribution of IP3R in canine pancreatic homogenates. IP3R was present primarily in a smooth microsomal fraction (low density), a (high density) rough microsomal (RM) fraction previously shown to consist of highly purified rough endoplasmic reticulum (RER) vesicles, and, to a much lesser extent, in an intermediate density microsomal fraction which did not contain markers for RER or plasma membrane. When the RM fraction was subjected to isopycnic centrifugation on sucrose gradients, IP3R equilibrated at high sucrose densities. When ribosomes were extracted from the RM fraction by treatment with puromycin/high salt, IP3R equilibrated at considerably lighter sucrose densities. This shift in density indicated that IP3R which was present in the RM fraction is associated with the RER. Because of a significant amount of IP3R fractionating into the smooth microsomal fraction (which contains plasma membrane, among other "smooth" membranes) and a considerable amount of IP3R present in the nuclear pellet which is also enriched in plasma membrane, we examined the possibility that IP3R may be present in plasma membrane. Further subfractionation of a crude plasma membrane pellet from rat liver revealed that IP3R coenriched with a plasma membrane marker and strongly suggested an association of IP3R with plasma membrane. The issue of why the same receptor is found in multiple biochemically and morphologically distinct membrane fractions is discussed in terms of the possibility of RER subcompartmentalization and IP3R subtypes. The fractionation pattern of IP3R in pancreas is significantly different from that previously reported for calcium (Ca2+)-binding proteins and an intracellular Ca-ATPase (Nigam, S. K. and Towers, T. (1990) J. Cell Biol. 111, 197-200), raising questions as to links between these latter proteins and IP3 sensitive Ca2+ pools. Nevertheless, although the fractionation patterns are different, all of these proteins are clearly associated with the RER.
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PMID:Inositol 1,4,5-trisphosphate receptors. Localization in epithelial tissue. 131 1

To maintain alveolar air spaces relatively fluid free, the alveolar epithelium appears capable of vectorial transport of water and solutes. Active transepithelial transport of sodium by alveolar epithelial cell monolayers has previously been demonstrated, indicating that alveolar pneumocytes must possess ion transport mechanisms by which sodium can enter the cells apically for subsequent extrusion via Na(+)-K(+)-adenosinetriphosphatase activity at the basolateral surface. In this study, sodium entry mechanisms were investigated by directly measuring 22Na uptake into rat alveolar epithelial cells grown in primary culture. Cells exhibited increasing 22Na uptake with time over a 30-min interval. Total sodium uptake was compared in the presence and absence of several sodium transport inhibitors. Uptake was inhibited by the sodium channel blockers amiloride and benzamil but was not affected by two amiloride analogues (bromohexamethylene amiloride and dimethylamiloride) with diminished specificity for blocking sodium channels and enhanced specificity for inhibiting the Na(+)-H+ antiporter. Uptake was also unaffected by the chloride transport inhibitor bumetanide or by the absence of glucose. These data suggest that sodium uptake occurs primarily via sodium channel and that Na(+)-H+ antiport, Na(+)-K(+)-2Cl- cotransport, and Na(+)-glucose cotransport do not contribute significantly to sodium uptake under these experimental conditions. The presence of sodium channels in the alveolar epithelial cell membrane may provide the major entry mechanism by which sodium enters these cells for subsequent active extrusion, thereby effecting net salt and water reabsorption from the alveolar spaces.
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PMID:Evidence for amiloride-sensitive sodium channels in alveolar epithelial cells. 131 1

Regulation of proximal tubular Na-K-adenosine-triphosphatase (ATPase), brush-border membrane Na(+)-H+ antiporter and Na(+)-Pi symporter activity by endogenously produced dopamine was examined in Wistar rats. Na-K-ATPase was measured in basolateral membrane (BLM) fractions permeabilized with alamethicin or sodium dodecyl sulfate (SDS). Carbidopa (5 mg/kg) injected 18 h before removal of kidneys increased maximal activity (Vmax) noncompetitively in cortical BLM but not in other membrane fractions or outer medullary BLM (-2 +/- 4%). Chronic renal denervation did not alter the response. Carbidopa stimulated Na-K-ATPase in cortical BLM from rats eating a normal salt diet with and without 1% saline to drink (+18 +/- 4% and +22 +/- 4%, respectively; P greater than 0.001). Carbidopa did not increase Vmax of BLM Na-K-ATPase from rats eating a low-salt diet (+1.5 +/- 4%); however, when the low-salt diet was supplemented with 1 mM dihydroxyphenylalanine (dopa) to drink for 1 day carbidopa, increased Vmax by 18 +/- 3% (P = 0.018). Carbidopa did not alter the Michaelis constant (Km) for Na or K or inhibitory constant (Ki) for ouabain. Injection of the DA1 antagonist Sch 23390 (2 mg/kg) also increased Na-K-ATPase (18 +/- 4%; P = 0.014). Western blots using a monoclonal alpha-subunit antibody revealed a 22 +/- 8% increase following carbidopa treatment (P = 0.033; n = 19 pairs). Carbidopa had no effect on Na(+)-H+ antiporter activity (22Na uptake) or on Na(+)-32Pi cotransport in brush-border membrane vesicles. These results indicate that dopamine produced in proximal tubules tonically reduces Na-K-ATPase Vmax by decreasing the number of alpha-subunits associated with the BLM.
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PMID:Proximal tubular dopamine production regulates basolateral Na-K-ATPase. 131 6

The freshwater cyanobacterium Synechococcus PCC 6311 is able to adapt to grow after sudden exposure to salt (NaCl) stress. We have investigated the mechanism of Na+ transport in these cells during adaptation to high salinity. Na+ influx under dark aerobic conditions occurred independently of delta pH or delta psi across the cytoplasmic membrane, ATPase activity, and respiratory electron transport. These findings are consistent with the existence of Na+/monovalent anion cotransport or simultaneous Na+/H(+)+anion/OH- exchange. Na+ influx was dependent on Cl-, Br-, NO3-, or NO2-. No Na+ uptake occurred after addition of NaI, NaHCO3, or Na2SO4. Na+ extrusion was absolutely dependent on delta pH and on an ATPase activity and/or on respiratory electron transport. This indicates that Na+ extrusion via Na+/H+ exchange is driven by primary H+ pumps in the cytoplasmic membrane. Cells grown for 4 days in 0.5 M NaCl medium, "salt-grown cells," differ from control cells by a lower vmax of Na+ influx and by lower steady-state ratios of [Na+]in/[Na+]out. These results indicate that cells grown in high-salt medium increase their capacity to extrude Na+. During salt adaptation Na+ extrusion driven by respiratory electron transport increased from about 15 to 50%.
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PMID:NMR studies on Na+ transport in Synechococcus PCC 6311. 131 38

An initial characterization of the lenticular ionic permeabilities of the isolated Sprague-Dawley rat lens utilizing short-circuiting techniques was carried out to provide the basis for further studies of mechanisms underlying cataractogenesis associated with salt-sensitive genetic hypertension in the rat. Both active and passive Na+ and K+ transport were evaluated by varying ionic concentrations in the bathing solutions facing the anterior and posterior sides of the lens, as well as by the addition of BaCl2 and ouabain. In general, the ionic permeabilities and transport properties of the rat lens are qualitatively similar to those previously described in other species. Ionic replacement studies showed the presence of Na+ and K+ channels at both surfaces of the lens, with the anterior side K+ conductance being larger than the posterior. In contrast, Na+ conductance was similar at both lens surfaces. The effects of ouabain confirmed the presence of the Na(+)-K(+)-ATPase at the lens epithelium, while the effects of serial addition of BaCl2 and ouabain suggested that the contribution of K+ diffusion to the short-circuit current may be considerably greater than the electrogenic component of the Na(+)-K+ pump.
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PMID:Characterization of active and passive Na+ and K+ transport in normal rat lens by the short-circuiting technique. 131 40

We examined the regulation of Na+,K(+)-ATPase activity in proximal tubule segments during a high salt diet in prehypertensive Dahl salt-sensitive and salt-resistant rats. Rats were placed on normal salt or high salt diets (0.9% saline as drinking water). During the normal salt diet, Na+,K(+)-ATPase activity was not different between Dahl salt-sensitive and salt-resistant rats. After 2 days and 10 days on a high salt diet, Na+,K(+)-ATPase activity in Dahl salt-resistant rats significantly decreased when compared to Dahl salt-resistant rats on a normal salt diet (P less than 0.01). The decreased Na+,K(+)-ATPase activity in Dahl salt-resistant rats during a high salt diet was reversed by treatment with an inhibitor of aromatic L-amino acid decarboxylase (dopamine synthesizing enzyme), benserazide. In contrast, Na+,K(+)-ATPase activity did not decrease during the high salt diet and benserazide had no effect on Na+,K(+)-ATPase activity in Dahl salt-sensitive rats. These results indicate that Dahl salt-sensitive rats do not have the capacity to down-regulate the proximal tubule Na+,K(+)-ATPase activity during a high salt diet. Indirect evidence suggests that the regulation of Na+,K(+)-ATPase activity by locally produced dopamine is absent in Dahl salt-sensitive rats.
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PMID:High salt diet down-regulates proximal tubule Na+, K(+)-ATPase activity in Dahl salt-resistant but not in Dahl salt-sensitive rats: evidence of defective dopamine regulation. 131 13

Regulation of the level of ionized calcium, [Ca2+]i, is critical for its use as an important intracellular signal. In cardiac and skeletal muscle the control of fluctuations of [Ca2+]i depend on sarcolemmal and sarcoplasmic reticulum ion channels and transporters. We have investigated the sesquiterpine lactone, thapsigargin (TG), because of its reported action to alter cellular calcium regulation in diverse cell types, including striated muscle cells. We have combined biochemical and physiological methods at the cellular level to determine the site of action of this agent, its specificity, and its cellular effects. Using a patch-clamp method in whole cell configuration while measuring [Ca2+]i with Indo-1 salt, we find that TG (100 nM) largely blocks the contraction and the [Ca2+]i transient in rat ventricular myocytes. Analysis of these data indicate that no sarcolemmal current or transport system is directly altered by TG, although indirect [Ca2+]i-dependent processes are affected. In permeabilized myocytes, TG blocked oxalate-stimulated calcium uptake (half-maximal effect at 10 nM) into the SR. However, TG (100 microM) had no effect on Ca(2+)-induced Ca(2+)-release in purified muscle (ryanodine-receptor enriched) vesicles while clearly blocking Ca(2+)-ATPase activity in purified (longitudinal SR) vesicles. We conclude that in striated muscle TG markedly alters calcium metabolism and thus alters contractile function only by its direct action on the Ca(2+)-ATPase.
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PMID:Thapsigargin inhibits contraction and Ca2+ transient in cardiac cells by specific inhibition of the sarcoplasmic reticulum Ca2+ pump. 132

To investigate the functional role of the different Na+, K(+)-ATPase alpha (catalytic) subunit isoforms in neuronal cells, we used quantitative in situ hybridization with riboprobes specific for alpha 1, alpha 2, and alpha 3 isoforms to measure the level of alpha isoform-specific expression in the neuroendocrine cells of the supraoptic (SON) and paraventricular (PVN) nuclei of rat hypothalamus. A prolonged increase in electrical activity of these cells, achieved by 5 days of salt treatment, increased the amount of alpha 1 isoform mRNA in the SON and PVN by 50%. Levels of alpha 1 mRNA in other brain regions and levels of alpha 2 and alpha 3 mRNAs were not affected by salt treatment. We conclude that the alpha 1 isoform Na+, K(+)-ATPase may be specifically adapted to pump out Na+, which enters the cells through voltage-gated channels during neuronal depolarization.
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PMID:Activity-dependent regulation of Na+, K(+)-ATPase alpha isoform mRNA expression in vivo. 132 Dec 32

A fundamental and essential property of nearly all salt-transporting epithelia is the tight parallel coupling between the magnitude of the K-conductive pathway at the basolateral membrane and the activity of the Na,K-dependent ATPase (Na,K-ATPase). In the present study, we demonstrate that the coupling response in the renal proximal tubule is governed, at least in part, through the interaction between ATP-sensitive K channels and Na,K-ATPase-mediated changes in intracellular ATP levels. First, we identified a K-selective channel at the basolateral membrane, which is inhibited by the cytosolic addition of ATP. Second, conventional microelectrode analysis in the isolated perfused proximal straight tubule revealed that these channels are the major determinant of the macroscopic K conductance so that ATP-mediated changes in the open probability of the K channel could alter the extent of K recycling. Indeed, the increase in the macroscopic K conductance upon stimulation of transcellular Na transport and pump activity was found to be paralleled by a decrease in intracellular ATP. Finally, a causal link between parallel Na,K-ATPase-K-channel activity and ATP was established by the finding that intracellular ATP loading uncoupled the response. With our recent observations that similar ATP-sensitive K channels are expressed abundantly in other epithelia, we postulate that ATP may act as a universal coupling modulator of parallel Na,K-ATPase-K-channel activity.
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PMID:ATP is a coupling modulator of parallel Na,K-ATPase-K-channel activity in the renal proximal tubule. 132 39

Ultrafiltrate obtained by hemodialysis of patients with uremia who were not taking cardiac glycosides was used as a source of Na, K adenosine triphosphatase inhibitor for purification and further study. Inhibitory activity was measured by a linked-enzyme assay and by effect on rubidium 86 uptake in guinea pig aortic strips. Two approaches were used in purification: dialysis with a 500 dalton membrane followed by gel filtration with Sephadex G-25, and removal of protein by acidification and boiling followed by Sephadex G-10. The first procedure failed to separate the inhibitor from the salt fraction, whereas the second separated the inhibitor from the salt peak but resulted in partial coelution of the inhibitor with endogenous pyruvate, which interferes with the linked-enzyme assay. Pooled, concentrated G-10 elution fractions from the early part of the inhibitor peak, which were free of pyruvate, produced a dose-response relationship by enzymatic assay that was close to parallel with that for ouabain. Like ouabain, these fractions also inhibited 86Rb uptake in guinea pig aorta. Despite these properties, our previous work has demonstrated that the inhibitor, unlike some other ouabain-like or digitalis-like substances obtained from blood or urine, has no apparent role in body fluid homeostasis.
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PMID:An Na, K ATPase inhibitor from ultrafiltrate obtained by hemodialysis of patients with uremia. 132 35


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